I had a thought about possible original plans for the faction war, based on how heavily the devs teased “Red Kalimdor and Blue Eastern Kingdoms” at Blizzcon 2017.
To add to what I said earlier–if I had to speculate, I’d guess that they envisioned a lot more battlefronts, with the war moving in different directions: almost-totally-red Kalimdor (except for Azuremyst Isle) and almost-totally-blue EK (except for Quel’thalas) in patch 8.2 or 8.3, and then counteroffensives leading to more or less the original territory borders by the end of the expansion.
That would tie in with this oddly specific and detailed exchange from the Blizzcon Q&A panel:
Jenny : Alright, another viewer would like to know: are the continents of Kalimdor and Eastern Kingdoms completely split between the factions; and what does that mean for places like Silvermoon city and the Exodar?
Alex : Well, Silvermoon and Exodar are still Alliance and Horde respectively. Those zone boundaries are very tricky for NPCs to cross. We will have a fiction in place, obviously.
Those two are kinda the last bastions of their factions, and maybe a way in for those factions as well, and we will be sure to use them in this battle.